Ceiling fans have become increasingly popular in today's homes and businesses. Ceiling fans are typically mounted to either a ceiling box or a ceiling pan. Ceiling boxes and ceiling pans are essentially identical, except that ceiling boxes are about 11/2 to 21/8 inches in depth and mounted to the side of a truss, joist or rafter, while ceiling pans are about 1/2 inch in depth and mounted to the bottom of a truss, joist or rafter. Thus, ceiling boxes are typically used in new work or construction, while ceiling pans are used in old work and new work applications. In old work applications, the ceiling pan eliminates the need to crawl in the attic for mounting it to the joist, which is necessary when using a ceiling box in old work applications.
In the past, ceiling boxes or pans were tested under static loads only. With the increasing popularity of ceiling fans came the concern that the dynamic loads of an unbalanced ceiling fan could cause the ceiling box or pan to flex and break. This concern led to a new 1987 N.E.C. code provision (N.E.C. 370-17C) that required ceiling boxes or pans intended to be used as the sole support of ceiling fans to be tested and listed for that use. Underwriter's Laboratories (U.L.) responded with a new test that ceiling boxes or pans are required to pass.
A plastic ceiling box or pan that withstands the dynamic flexing of an unbalanced ceiling fan and resists torque loads is not known in the prior art. However, because plastic electrical boxes are relatively inexpensive and easy to manufacture, it would be desirable to use plastic ceiling boxes for fan support.
U.S. Pat. No. 3,701,448 to Vadnais discloses a metallic electric junction box having an identification on one side so that the box can be fit over a corrugation or ridge in a roofing panel. By wrapping around the corrugation, the box resists tilting when a heavy fixture is being installed. The Vadnais patent does not disclose a plastic ceiling box which resists the dynamic flexing produced by an unbalanced ceiling fan.
Examples of other electrical outlet boxes known in the art are disclosed in the following U.S. Pat. Nos.: 1,966,451 to Manquais, 1,800,484 to Thomas, and 1,748,693 to Adell.
None of these patents are directed to special problems of flexing and breaking associated with plastic ceiling fan boxes required to withstand torque loads from fan blades or other dynamic motions.
This invention addresses these problems in the art, along with other needs which will become apparent to those skilled in the art once given this disclosure.